The present invention relates to a digital color copier, printer or similar image forming apparatus of the type capable of forming a plurality of different images at the same time and more particularly to an image forming apparatus capable of reducing capacity required of a memory and enhancing the productivity of images.
An image forming apparatus of the type described uses an ADF (Automatic Document Feeder) for continuously feeding two of a plurality of documents to a glass platen included in a document feeding unit. Specifically, the ADF conveys two documents to the document reading unit at an interval corresponding to an interval between papers fed one by one, so that the leading edge of the image of the second document meets and that of the second paper meet each other.
In practice, however, a preselected density pattern is formed, during the interval between papers, on a photoconductive element carrying a toner image thereon for the purpose of controlling, e.g., the toner content of a developer. Specifically, a density sensor senses the density of the preselected pattern to see if a toner image is formed with adequate density or not. Generally, therefore, the interval between documents fed by the ADF is greater than the interval between papers, increasing the range that the document reading unit has to read. As a result, the image reading unit and therefore the entire image forming apparatus is bulky.
In light of the above, image data read by the document reading unit out of two consecutive documents may be written to a page memory and then read out at a timing so adjusted as to cause the leading edge of each image to meet the leading edge of a particular paper. This kind of scheme, however, needs an expensive memory having a capacity great enough to accommodate the image data of two documents.
To solve the above problem, as soon as the document reading unit reads the entire first document, it may stop its reading operation and resume it at the time when the second document is fed from the ADF. This is also successful to cause the leading edge of the second document and that of the second paper to meet each other. However, causing the document reading unit to stop its operation and then resume it is time-consuming and cancels the advantage of the simultaneous formation of two document images, i.e., high-speed image formation.
It is therefore an object of the present invention to provide an image forming apparatus having a miniature configuration and capable of enhancing the productivity of image formation without resorting to a large capacity memory.
In accordance with the present invention, an image forming apparatus includes a photoconductive element for forming a toner image thereon. An intermediate image transfer body is provided with a plurality of reference marks defining reference positions for the transfer of the toner image. The intermediate transfer body is capable of simultaneously holding two different toner images of a reference image size transferred from the photoconductive element. The two toner images are transferred from the intermediate image transfer body to two consecutive papers fed one by one. A document reading unit sequentially reads two documents of the reference image size sequentially fed from an ADF. When the document reading unit reads the two documents, a controller stores image data representative of a second document in a delay memory. After a first document has been read, the controller outputs the data of the second document by delaying the image data by a period of time corresponding to a difference between an interval between the papers and an interval between the documents.
Also, in accordance with the present invention, an image forming apparatus includes a photoconductive element for forming a toner image thereon. An intermediate image transfer body is provided with a plurality of reference marks defining reference positions for the transfer of the toner image. The intermediate image transfer body is capable of simultaneously holding two different toner images of a reference image size transferred from the photoconductive element. The two different toner images are transferred from the intermediate image transfer body to two papers fed one by one. A document reading unit sequentially reads two documents of the reference image size sequentially fed from an ADF at a preselected interval. When the document reading unit having read first one of two documents starts reading the next document, a controller stores image data representative of the next document by delaying them by a period of time corresponding to a difference between an interval between papers fed one by one and an interval between the documents fed from the ADF.